Businesses which have adopted RF Local Area Networks (LAN) transmit data using RF communications. FIG. 1 illustrates a typical RF packet transmission system comprising a wireless LAN in which control module (CM) 10 utilizes RF communications to communicate with a plurality of user modules (UM) 12. Each UM 12 is connected to one or more user devices 14 such as a terminal, personal computer or other information input/output device via connection 16. The CM 10 is connected to data network 18 by data channel 20 which may include, but is not limited to wires or optical links.
The CM 10 controls communications within the illustrated network and passes information from data network 18 to user devices 14 via an associated UM 12. The CM 10 also controls local communications by receiving information from one UM 12A and relaying the information to a different UM 12B. Data network 18 may consist of an Ethernet network, a Token Ring network, or any of the other of the well known data networks.
In the packet transmission system of FIG. 1, information such as the information passed between UM 12 and a user device 14 or between CM 10 and data network 18, is conveyed in the form of data packets multiplexed into a data stream. Wireless information such as the information transmitted between UMs 12 and CM 10, is conveyed in the form of radio transmission packets. Each radio transmission packet typically contains a preamble and an information field. The preamble may comprise control data, synchronization information and/or destination device information. The information field contains at least some of the information comprising a data packet.
By way of example, assume two terminal devices 14 serviced by a common UM 12 transmit an equal number of packets, N/2, over wire 16. Further assume that N is 10. Then each terminal device 14 connected to UM 12 will transmit 5 packets which collectively combine to create the multiplexed data stream 300 of FIG. 3.
Continuing with this example, a first terminal device 14, designated as terminal A, transmits 5 packets numbered 0-4, while a second terminal 14, designated as terminal B, transmits 5 packets numbered 0-4. When transmitted over the wire 16, these 10 packets A0-A4 and B0-B4 are typically interspersed in a random nature, such as: B0,B1,A0,B2,A1,A2,A3,B3,A4,B4. While the data stream ordering appears completely random, it will be noticed upon closer inspection that this ordering is actually pseudorandom, for data packets A0-A4 and B0-B4 maintain their original and sequential order with respect to the source devices A and B, respectively. Consequently, packet A0 will always precede packets A1-A4 in ascending order while packet B0 will always precede packets B1-B4 in the same ascending order.
It will of course be appreciated by those skilled in the art that the preceding discussion is presented, in part, for illustrative purposes. Any number of terminal devices 14 can be serviced by UM 12. The number of data packets transmitted by those terminal devices may vary. Moreover, the data stream length N can be any number of data packets. Despite these variances, data stream packets maintain a sequential relationship (0,1,2,3, . . . , N) with respect to their source or point of origin.
During the transmission of radio transmission packets that convey data stream packets between UMs 12 and CM 10, it is extremely likely that the data stream packet order will change as a result of RF anomalies such as multipath reception and radio interference. This is especially true of the in-building office environment envisioned by the packet transmission system of FIG. 1. In such an environment, RF anomalies may result in lost, delayed or unintelligible radio transmission packets. As received by CM 10, a reconstructed data stream may only comprise, for example, data packets A1,B0,A4,B3,A2,B4,A0,B1,B2.
Where packet data network 18 of FIG. 1 employs data messaging protocols capable of handling reordered data packets, the reconstructed data stream A1,B0,A4,B3,A2, B4,A0,B1,B2 may be transmitted over channel 20 for further processing. If, on the other hand, packet data network 18 employs data messaging protocols which are catastrophically sensitive to the receipt of data packets from a terminal device 14 which no longer have their original sequentially ordered relationship (A0-A4 or B0-B4), successful processing and ultimately system operation will fail.
Examples of data messaging protocols which are catastrophically sensitive to the receipt of reordered data packets include, but are not limited to:
High Level Data Link Control (HDLC); PA0 Link Access Protocol-B (LAP B); PA0 Link Access Protocol-D (LAP D); PA0 Logical Link Control II (LLC II); and PA0 Synchronous Data Link Control (SDLC).
While the prior art suggests that lost and/or corrupted radio transmission packets can be retransmitted, the incident delays adversely impact system throughput. This is especially true where multiple users devices 14 are supported by a single UM 12. Since the above mentioned data messaging protocols are widely used in the field of data communications, it would be extremely advantageous to provide a method whereby lost, unintelligible, or delayed radio transmission packets associated with a specific user device 14 do not interrupt service to the other devices 14 supported by the common UM 12.